A significant problem in the mass production of a multiple contact spring switch is the difficulty of consistently obtaining, (1) the design spacing between contact springs when the switch is open, (2) the design timing of the closure of the contact springs relative to the movement of an associated actuator, and (3) the design contact force when the switch is closed.
Illustrative of the problem is the transfer switch disclosed in Baldasare Pat. No. 3,177,207. The switch comprises a movable cantilever contact spring that is situated between two stationary cantilever contact springs. The lower ends of the contact springs are interleaved with insulating separators and secured to a mounting strip. The upper ends of the stationary contact springs are free-standing and are deformed to extend at an angle to the lower ends. The upper end of the movable contact spring is tied to an actuator spring by an insulating spacer, and the actuator spring is itself biased against a cam surface on a pushbutton plunger. The pushbutton plunger is linearly displaceable between two positions, and the interaction between the actuator spring and the cam surface is such that in one position of the pushbutton plunger, the movable contact spring is in engagement with a first of the stationary contact springs and spaced from the second stationary contact spring. In the other position of the pushbutton plunger, the location of the movable contact spring is reversed.
The upper and lower ends of the pushbutton plunger are respectively slidably supported on a bearing bar and a bottom strip, which are discrete elements that are joined to one another by other discrete elements. In addition, the mounting strip to which the contact springs are secured is in turn secured to the bottom strip. Thus it is seen that the location of the movable contact spring with respect to the stationary contact springs varies from switch to switch in accordance with tolerance variations in the pushbutton plunger, the bearing bar, the bottom strip, the mounting strip, the actuator spring, the plurality of insulating separators, the insulating spacer, and the movable and stationary contact springs. Therefore, if the switch is manufactured on a mass production basis, it is exceedingly difficult to obtain consistency of spacing, contact force, and timing, and manual adjustment of the contact springs is necessary after they are assembled.
An improvement over this arrangement is disclosed in Stow et al. U.S. Pat. No. 3,626,131. Stow discloses a pushbutton switch comprising a hollow case having a collar within which a pushbutton plunger is slidably displaceable. The case is snap-mounted to a base having a pair of cantilever contact springs mounted thereon and the free ends of the contact springs are respectively biased against individual cam surfaces on the plunger. The cam surfaces are arranged such that the contact springs are normally separated, but when the plunger is depressed, one of the springs is deflected outwardly into engagement with the other contact spring. Thus the switch has fewer elements than that of Baldasare, resulting in less tolerance buildup, and the position of the contact springs with respect to one another is determined by the cam surfaces on the plunger.
However, both contact springs have a convoluted configuration. A first of the contact springs comprises a bent bearing end for engaging the cam surface, an inclined stem section, a horizontal mounting section, and a vertical terminal section. The other contact spring comprises a horizontal contact section that overlies the stem section, a horizontal mounting section, and a vertical terminal section. The convoluted shapes of the contact springs require a number of forming operations and each such operation introduces another tolerance variation from spring to spring. As a result, it is likely that manual adjustment of the contact spring is necessary if there is to be a consistency between switches in the contact force and in the timing of the closure responsive to the actuation of the plunger.